fix(pg): emit query error even when callback is present

[mikemasam]

Issue: Query.handleError swallowed the 'error' event whenever
query.callback existed (always true with query_timeout or connectionParameters.query_timeout). listeners with on('error') never fired.

Fix: emit 'error' first if there are listeners, then still
invoke callback:

• guarded by listenerCount('error') so callback/promise-only
  don't throw an unhandled-'error'.
• preserves existing return callback(err) semantics.
• now matches with success path (callback + 'end');

Test: unit test verifies both callback and 'error' listener fire
for the same handleError.